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OWC Mercury Elite On-The-Go External SSD

September 13, 2009

This review is of the OWC Mercury Elite On-The-Go containing the Crucial M225 256GB solid state drive (SSD), perfect for a reliable, quiet, and fast solution when traveling.

Taking a photography trip to Antarctica or Africa? Why risk your trip on a fragile hard drive— consider a solid state drive for both internal and external use with a MacBook Pro, and reduce the odds of failure. Anyone whose time or work is valuable should be moving to a solid state drive for critical jobs when traveling, to reduce the risk of data loss from hard drive failure.

A 256GB-capacity model is not required; wallet-friendly 64GB and 128GB models are also available, while still retaining all the performance and desirable characteristics. As this review was being written, prices jumped on solid state drives by about 10%. Perhaps they’ll come down later in 2009; SSD has a bright future. View prices on SSD

The Crucial 256GB solid state drive (SSD) was previously tested as an internal SATA device in a Mac Pro and found to be an outstanding performer. See also How to Make Your Mac Feel Lightning-Fast.

Note: any laptop SSD or hard drive works in the OWC Mercury Elite On-The-Go case.

Why choose a solid state drive?

The SSD at left, the On-The-Go enclosure at right
(can be purchased pre-assembled)

Unlike a hard drive, a solid state drive(SSD) is made up of memory chips for storage. It offers multiple desirable characteristics besides high performance:

  • low power consumption;
  • silent operation;
  • superior impact resistance;
  • can be operated at very high altitudes (12,000 feet on up), where hard drives are at risk;
  • no moving parts to fail;
  • reliability!

Don’t underestimate the “impact resistance” advantage: while assembling the unit, I dropped the drive two feet onto a hardwood floor, a disaster for a hard drive, but a non-event for the SSD. Could that happen to you on an important trip, destroying not just your files, but the hard drive itself? Dropping a portable drive is not even a “black swan” event; it’s more of a gray or dingy white!

Performance externally

Performance of a solid state drive (SSD) in an external enclosure will be limited to the speed of the connection bus in terms of transfer rate: slower than with an internal SATA connection. The On-The-Go enclosure supports Firewire 800/400 and USB 2.0.

Even though sustained transfer rate is slower using Firewire 800 as compared to an internal SATA drive, performance will still be very satisfying because there is very low latency and no seek time as with a hard drive. Also, an SSD does not slow down as it fills up (though over time really intense use can result in internal fragmentation).

On-The-Go enclosure

The On-The-Go enclosure was originally designed for laptop hard drives, with a large heat sink at bottom for cooling. To my surprise, the 256GB Crucial unit actually heated up just like a hard drive, so it appears that the heat sink remains desirable.

A more compact case would be a nice plus; it fits into a large pocket but is larger than it really needs to be. Perhaps the future will bring not only a slimmer design, but a quad-interface model with an eSATA port for higher performance and greater versatility.

The unit is supplied with cables and a carrying case.

Bus powered

A really nice plus of using the Firewire 800/400 or USB cable is that the drive is bus-powered— power is drawn from the Firewire 800 cable, so all that’s needed is the drive and a short cable— very convenient for travel.


You can purchase the SSD and On-The-Go enclosure separately. Assembly requires a small philips screwdriver.

If you are assembling the unit yourself, you can download the assembly instructions as a PDF. If you don't already have a nice computer-friendly toolkit, I recommend the Newer Technology 11-Piece Portable Toolkit.

If you want a more compact unit, you can actually leave the external shell off, at a small risk of some static electricity (most parts are fully protected even without the external shell)—I’m not recommending doing so, but it’s an option.

Upgrade Your Mac Memory
At much lower cost than Apple, with more options.

Lloyd recommends 64GB for iMac or Mac Pro for photography/videography.


The comments here are with the drive used via Firewire 800, the highest performance way to connect the On-The-Go unit. You can also use USB 2.0 or Firewire 400 if you must, but they’ll be slower.

Testing was with Mac OS X Snow Leopard 10.6.1.

Firewire 800 speed

Mac OS X has long had poor write performance with Firewire, and sadly, Snow Leopard doesn’t appear to fix that problem entirely, at least not in my testing here. The best one can expect from Firewire 800 for reads is about 85MB/sec, and perhaps 80MB/sec for writes (usually more like 60MB/sec).

On the MacBook Pro

Booting the MacBook Pro 2.93GHz off the On-The-Go-SSD proved to be a very enjoyable experience. The MacBook Pro used for this test has the fastest currently available hard drive internally, the 500GB Seagate 7200.4. Yet launching applications like Adobe Photoshop and Adobe Lightroom was much faster with the On-The-Go-SSD.

Here is what I observed for sustained transfer speed on the MacBook Pro 2.93GHz using DiskTester. These times are about as fast as I’ve ever observed for a single drive!

disktester run-sequential --test-size 32GB --chunk-size 32MB:

Write: 72.8 MB/sec
Read:  85.3 MB/sec

On the Mac Pro

I was prepared to be disappointed when booting my Mac Pro using the drive using Firewire 800. And clearly the drive is not quite as fast running over Firewire 800 as compared to SATA on an internal Mac Pro port.

But instead of being disappointed, I found that booting the Mac Pro and launching applications was very responsive and clearly superior to using a hard drive. Read speed is what counts for those activities, and with no latency and no seek time, the SSD really delivers.

Here is what I observed for sustained transfer speed on the Mac Pro Nehalem using DiskTester. These times are quite good for Firewire 800, but not as good as the times observed with the MacBook Pro, above.

disktester run-sequential --test-size 32GB --chunk-size 32MB:

Write: 63.7 MB/sec
Read:  81.8 MB/sec

Conclusions and recommendations

Trusted vendor OWC

See also the On-The-Go reviewed with a hard drive.

The OWC Mercury Elite On-The-Go with the Crucial M225 256GB is about as good as it gets for a portable storage solution (models with 64GB and 128GB and 256GB capacity are also available).

I highly recommend this unit to anyone concerned about reliability and/or peformance with a MacBook Pro when traveling. Photographers will be delighted with units performance and the extra comfort in knowing the unit can take some accidental impact without any negative effects.

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